1. Field of the Invention
The present invention relates to a system diagnostics and control system for an apparatus having an induction motor and a heater and more particularly to a control for a clothes dryer having a split phase induction motor wherein operations of the dryer are controlled in response to phase angles of the motor and in response to one or more temperature sensors.
2. Description of the Prior Art
A control system for motors and for various appliances with motors is shown in U.S. Pat. No. 4,481,786, issued Nov. 13, 1984, and entitled ELECTRONIC CONTROL FOR A DOMESTIC APPLIANCE (Bashark I). The control system employes a ferrite core sensor having a primary winding that is formed of two turns of the run winding of the motor, typically an AC induction drive motor. The sensor has a single turn secondary winding that forms a sense winding coupled to a motor phase monitoring circuit. The sense winding provides a signal representing a polarity change in the run winding current. The current polarity change signal is used by the motor phase monitoring circuit to provide a voltage compensated motor phase angle angle pulse to a microcomputer for the appliance to control various operations of the appliance.
In particular, Bashark I teaches a control for a dryer wherein a digital representation of the motor phase angle pulse is used by the microcomputer to monitor the operation of the motor under the loading created by the clothes being tumbled in the dryer drum. The motor phase angle representation is used by the microcomputer to calculate a clothes tumble number by summing the absolute difference between given sums of the phase angle representations which are then used to generate a control signal at a given tumble number threshold for terminating the operation of the motor.
Bashark I also teaches that the same or a similar control circuit may be used to monitor the motor of other appliances, such as an air conditioner, a dishwasher, an automatic washer, and a refrigerator and to provide other types of information about the operation of these appliances. However, the disclosure in Bashark I was limited to monitoring only motor characteristics and was further limited in the types of information obtained from analyzing the phase angle information and the types of functions controlled as a result of obtaining the phase angle information. Furthermore, Bashark I used only the single motor sensor and did not suggest how additional information could be obtained from other sensors advantageously interacting with the motor phase angle sensor. The present invention is directed to providing these advantageous features to the control as well as providing various additional improvements to motor sensors and controls generally.
It is known to use various single purpose sensors to monitor the condition of a dryer or the clothes load within the drum of the dryer. For example, it is known to detect a blocked lint filter using fluid pressure measurements, as shown for example in U.S. Pat. No. 3,286,508, or by detecting the passage of light through the filter, as shown for example in U.S. Pat. No. 3,484,772.
It is also known to use various single purpose sensors to monitor the dryness of the clothes load in a dryer. For example, it is known to detect dryness by detecting the conductivity of the clothes using a pair of electrode sensors, as shown for example in U.S. Pat. No. 3,593,571, or by discharging a capacitor into the clothes, as shown for example in U.S. Pat. No. 4,422,247. Still another technique is to measure exhaust air temperature, as taught by U.S. Pat. No. 3,203,679. This dryness information is either used directly or indirectly to control the length of a drying cycle or the energization of the heater. In U.S. Pat. No. 4,385,452, for example, a microcomputer seeks a preset number of consecutive "dry" readings from the sensor before it will act to regulate the drying cycle.
Still other sensors and controls are known in the art for controlling dryers. In U.S. Pat. No. 3,507,052, a dryer control is described which senses a load tumbling pattern and uses this information to set the speed of the motor so as to provide an optimum tumbling pattern. In U.S. Pat. No. 3,874,089, a dryer control is described which senses the energization of the heater and uses this information to control the motor.
Each of these prior art designs uses a single type of sensor to monitor a single characteristic and to control a single function of the dryer. None of these references provide a control circuit that is adapted for monitoring the function of the motor and the heater using a single circuit to monitor several diverse characteristics of the operation of the dryer and top provide complete control of the dryer operation.